Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A diagrammatic representation of a conventional disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16. The disk drive 10 also includes a cover plate (not shown) that is coupled to the base plate 16 and encloses the disk 12 and actuator arm assembly 18.
The actuator arm assembly 18 includes a flexure arm 20 attached to an actuator arm 22. A transducer 24 is attached to the end of the flexure arm 20. The transducer 24 is constructed to magnetize and sense the magnetic field of the disk 12. The actuator arm assembly 18 pivots about a bearing assembly 26 that is mounted to the base plate 16.
Attached to the end of the actuator arm assembly 18 is a magnet 28 located between a pair of coils 30. The magnet 28 and coils 30 are commonly referred to as a voice coil motor 32 (VCM). The spindle motor 14, transducer 24 and VCM 32 are coupled to a number of electronic circuits 34 mounted to a printed circuit board 36. The electronic circuits 34 typically include a read channel chip, a microprocessor-based controller, a random access memory (RAM) device, a voice coil motor driver, and a spindle motor driver.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding transducers 24 mounted to flexure arms 20 for the top and bottom of each disk surface. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
The flexure arm 20 is manufactured to have a bias such that if the disk 12 is not spinning, the transducer 24 will come into contact with the disk surface 12. When the disk is spinning, the transducer 24 typically moves above, or below, the disk surface at a very close distance, called the fly height. This distance is maintained by the use of an air bearing, which is created by the spinning of the disk 12 surface such that a boundary layer of air is compressed between the spinning disk 12 surface and the transducer 24. The flexure arm 20 bias forces the transducer 24 closer to the disk 12 surface, while the air bearing forces the transducer 24 away from the disk 12 surface. Thus, the flexure arm 20 bias and air bearing act together to maintain the desired fly height when the disk 12 is spinning.
It will be understood that if the disk 12 is not spinning at a high enough RPM, the air bearing produced under the transducer 24 may not provide enough force to prevent the flexure arm 20 bias from forcing the transducer 24 to contact the disk 12 surface. If the transducer 24 contacts an area on the disk 12 surface that contains data, some of the data may be lost. To avoid this, the actuator arm assembly 18 is generally positioned such that the transducer 24 does not contact a data-containing area of the disk 12 when the disk 12 is not spinning, or when the disk 12 is not spinning at a high enough RPM to maintain an air bearing.
In a load/unload (L/UL) drive, the actuator arm assembly 18 is positioned such that a tab on the end of the flexure arm 20 near the transducer 24 contacts a ramp. FIG. 2 shows a front perspective representation of a ramp structure 40. As depicted by FIG. 2, a tab 42 located at the end of the flexure arm 20 contacts a ramp 44 as the actuator arm assembly 18 is moved into position on the ramp while the disk is still spinning. This positioning of the actuator arm assembly 18 on the ramp 44 keeps the transducer 24 from contacting the disk 12 surface, thus helping avoid data loss. The use of a ramp 44 may also make more of the disk 12 surface available for storing customer data, as opposed to a contact start stop (CSS) drive, which will be discussed below. However, the use of a ramp 44 may also result in the actuator arm assembly 18 not being able to move the transducer 24 over some portion of the disk 12 surface. This is because the ramp 44 may extend over a portion of the disk 12 surface, thus limiting the movement of the actuator arm assembly 18. Thus, while the entire area of the disk 12 surface could be written to if accessible, the transducer 24 may not be able to physically access some portions of the disk area, thus making it beneficial to make the ramp 44 as short as possible.
In a CSS drive, the actuator arm assembly 18 is positioned such that the transducer 24 is parked in a landing zone when the disk 12 is no longer spinning. FIG. 3 shows a representation of a disk 12 with a landing zone 50. The landing zone 50 is an area on the disk 12 surface that does not contain customer data and is designed to allow a transducer 24 to contact the disk surface. Typically, the landing zone 50 is a textured area on the disk. This area is textured in order to reduce the surface area of the transducer that comes into contact with the disk surface, thus reducing stiction problems when the disk begins to spin, as is well-known in the art. While a CSS drive does not require a ramp, it does require that a portion of the disk 12 area be available as a landing zone 50. The use of a landing zone 50 thus reduces the amount of data that a disk may store.
In normal operation, when a disk drive 10 is shut down, the control electronics 34 operate to position the actuator assembly 18 such that the transducer 24 does not contact the data containing portion of the disk 12 surface when the disk 12 stops spinning. Additionally, in normal operation, when the transducer 24 is clear of the data containing area, the control electronics 34 brake the disk 12 to stop its spinning.
Braking the spinning disk 12 is necessary because the shaft, which rotates the disk 12, is connected to the base plate 16 using a low friction bearing assembly, and would take a very long time to stop spinning if left to coast to a stop. It is beneficial to stop the disk 12 from spinning for several reasons. For example, in a CSS drive the transducer 24 contacts the disk 12 surface, thus it is beneficial to minimize the amount of time the transducer 24 is in contact with the disk 12 surface while the disk 12 is spinning. Additionally, when a disk drive 10 is powered down, it is considered non-operational. When a disk drive is non-operational, typical specifications allow the shock levels that the disk drive is able to withstand to increase, often up to levels which may result in a transducer 24 contacting the disk 12 surface. For example, in a CSS drive, the non-operational shock levels may be at a level which would allow the transducer 24 to lift from the disk 12 surface and then contact the surface again, and in some L/UL drives the actuator arm 22 may be positioned in such a manner that the transducer 24 may contact the disk 12 surface in such a situation. Therefore, it is beneficial to slow the spinning disk 12 to a stop upon powering down the disk drive so that, if a non-operational shock as described above causes the transducer 24 to contact the disk 12 surface, the area on the disk 12 surface that the transducer 24 contacts is minimized. Furthermore, some drives use latches to secure the actuator arm assembly 18 when the disk drive is powered down, as will be discussed in more detail below. In some of these drives, the latch is activated dependant upon the speed of the rotating disk. In such a situation, the spinning disk 12 may draw the parked actuator arm assembly 18 back off of the ramp. Additionally, movement of the disk drive after it is shut down may cause the actuator arm assembly 18 to move and the transducer 24 to come back out over the data containing surface and contact the surface of the disk 12. Any of these events may result in the loss of customer data.
The brake is applied by shorting the windings of the spindle motor 14. Since the spindle motor 14 is typically a three-phase motor, shorting the windings of each phase generates a force that acts against the spinning motor, and thus the motor and disk slow to a stop.
In certain situations, a disk drive 10 may lose power while a transducer 24 is flying over the disk 12 surface where customer data is stored. Such situations may, for example, include a loss of power to the computer system containing the disk drive, a power supply malfunction within the computer or disk drive, or an inadvertent disconnect of the power to the disk drive prior to the drive being shut down. In order to reduce the chances of data being lost in such situations, methods and apparatuses have been developed which position the actuator arm assembly 18 such that the transducer 24 will not contact the data-containing portion of the disk 12 surface. Additionally, it is preferable in such a situation to brake the disk 12, in order to slow it from the high RPM that it was spinning at prior to the loss of power, for the reasons discussed above.
One conventional method for parking the transducer 24 and braking the disk 12 when the disk drive loses power will now be described. Typically, loss of power to the drive is detected by using a power supply monitor circuit located within the control electronics 34. This power supply monitor includes an undervoltage detector, which monitors the power supply to the disk drive. If the power supply to the disk drive drops below a specified level, the undervoltage detector acts to reset the electronics within the drive, and actuate a retract circuit to place the actuator assembly into an automatic park cycle, which will be described in more detail below. Once the automatic park cycle is complete, a brake cycle is initiated to slow the spinning disk. This braking is typically achieved by shorting the windings of the spindle motor, as described above.
The retract circuit is typically contained within the electronic circuits 34, and is powered using the back electromotive force (BEMF) generated from the windings of the spindle motor 14. When the automatic park cycle is initiated, the retract circuit is electrically connected to the windings of the spindle motor 14. If the motor is spinning at a high enough RPM, the voltage produced on the windings can be used to operate the retract circuit. The retract circuit actuates the VCM 32 and parks the actuator arm assembly 18 to clear the transducer 24 from the area of the disk 12 surface which contains customer data. Once the actuator has been parked a latch is used to secure the actuator arm assembly 18 on the ramp or in the landing zone, thus helping to avoid any data loss. The latch is typically located at the end of the actuator arm assembly 18 near the VCM, and prevents the actuator arm assembly 18 from moving after the latch is activated.
There are a number of common latch types including magnetic, inertial, and air vane, which are well understood by those of skill in the art. Some types of latches are activated by the rotation of the spindle motor. For example, the air vane latch uses the air flow from the spinning disks to open the latch. Another example is the eddy current latch which uses an eddy current created by the spinning motor hub to open the latch. These types of latches are typically activated when the disk RPM falls below the operation RPM by a preset level. This leaves the possibility of the actuator arm assembly 18 dropping off of the ramp or coming out of the landing zone after the automatic park cycle and before the disk RPM has slowed enough to activate the latch. Thus, it would be advantageous to both brake the disk, and provide power to the retract circuit to help prevent the actuator arm assembly 18 from moving prior to the latch activating.
Another solution, used in L/UL drives, to the potential problem of the actuator arm assembly 18 being drawn back over data containing areas of the disk, is the use of a detent. This solution uses a ramp with a depression, or a bump, which helps to prevent the actuator arm assembly 18 from being pulled back off of the ramp while the disk is spinning. However, the use of a detent on the ramp of a L/UL drive requires a longer ramp compared to a ramp with no detent. Additional ramp length can reduce the available area on a disk surface that may be used to store data. Thus, it would be advantageous to reduce or eliminate the detent on such a ramp.
In addition to the problems described above, in certain situations, the BEMF generated by the spinning disk may not generate enough voltage to power the retract circuit. In such a situation, the actuator arm assembly 18 may not be properly retracted, and the transducer 24 may come into contact with a portion of the disk 12 containing customer data. Such a situation may arise, for example, when the spindle motor 14 operates using a 5 Volt driver. Due to the lower voltage of the driver, the BEMF generated from the spinning disk is reduced as compared to a spindle motor 14 which uses a 12 Volt driver. In this situation, the voltage needed to activate the VCM 32 and move the actuator arm assembly 18 may be more than the available BEMF from the spindle motor 14. Thus, it would be advantageous to be able to perform a retract function with the reduced available BEMF from a 5 Volt driver.
Another situation in which the BEMF generated by the spinning disk may not generate enough voltage to power the retract circuit may arise in a CSS drive. In a CSS drive, it is often advantageous for the transducer 24 to come out of landing zone 50 at about one-half of the final disk RPM. This is advantageous because the landing zone 50 of a CSS drive is typically textured to prevent stiction, and the height of the textured surface can be greater than the flying height. Therefore, the transducer 24 does not really “fly” when it is located over the landing zone 50. By moving the transducer out of the landing zone 50 prior to the disk being at its final RPM, transducer contact with the landing zone 50 surface is reduced. Additionally, by moving the transducer out of the landing zone 50 at reduced disk RPM, the spindle motor 14 does not need to be designed to run with the increased friction which would result from the transducer 24 contacting the landing zone 50 surface until the disk is at full RPM. However, if power is lost after the transducer 24 has left the landing zone 50, but prior to the disk spinning up to full RPM, the full BEMF voltage is not available to do a retract. This reduced BEMF may not produce enough voltage to power the retract circuit and park the actuator arm assembly 18 on the ramp or in the landing zone 50. Again, it would be advantageous to be able to perform a retract function with reduced available BEMF.
One method of overcoming these potential voltage shortages is to use a second output stage with very a low overhead full wave rectification circuit that drives the VCM 32 during power down. However, this requires additional circuitry for the second output stage, and results in an output voltage nearly equal to the voltage available at the spindle motor 14 windings. This additional circuitry adds cost to the electronic circuitry, and takes up valuable area within the electronic circuitry. This additional circuitry may also increase manufacturing costs and, hence, the cost of disk drives to consumers. Thus, it would be advantageous to provide adequate voltage to perform the retract function in a 5 Volt drive or a slowly spinning disk without requiring significant additional circuitry beyond what is currently available within the control electronics. It would also be advantageous to provide voltage to the retract circuit which is greater than the BEMF voltage available at the spindle motor 14 windings.
Accordingly, there is a need to develop a method and apparatus for use during a power loss to a disk drive which: (1) reduces the instances of the actuator arm assembly being drawn over data containing areas of the disk, (2) provides the ability to keep the actuator arm parked while also braking the disk, (3) provides the ability to perform a retract function with reduced available BEMF without the need for significant additional circuitry, and (4) provides the ability to generate voltage to retract circuit which is greater than the available BEMF voltage.